Electrode for the electrochemically fineboring workpieces and method for producing the same

ABSTRACT

The invention relates to an electrode for the electrochemical fine-boring of workpieces, comprising an (electrode) tube ( 6 ) for an electrolyte ( 4 ) to pass through to reach a workpiece ( 5 ) which is to be machined, and an electrical conductor which is connected to the electrolyte ( 4 ), in which electrode the tube ( 6 ), for the purpose of boring bores with the smallest possible diameter, consists of a metal with a substantially amorphous structure, is electrically conductive and is provided on its outer surface, at least in sections, with a nonconductive insulating layer ( 10 ) (FIG.  2 ).

[0001] The invention relates to an electrode for the electrochemicalfine-boring of workpieces, comprising an (electrode) tube for anelectrolyte to pass through to reach an electrically conductiveworkpiece which is to be machined, and an electrical conductor which isconnected to the electrolyte, and to a process for producing anelectrode for the electrochemical fine-boring of workpieces.

[0002] A known electrode for electrochemical boring comprises a glasstube which is secured in a holding device, consists of SiO₂ glass andthrough which an electrolyte flows. The electrolyte is brought intocontact, through an opening in the glass tube which lies opposite theholding device, with the area of a workpiece which is to be machined byboring. In the glass tube, there is an electrical conductor, to which anegative electric charge is applied via a DC source. The opposite,positive charge is applied to the workpiece, so that a chemical reactionleads to material being eroded at the area of the workpiece which is tobe machined. The electrical conductor generally consists of a metal,such as a platinum wire.

[0003] A drawback of this arrangement is that when using glass tubes,the electrochemical boring is only able to produce holes or bores with aminimum diameter of 0.2 mm. Moreover, the electrode comprising a glasstube and wire arranged therein is of relatively complicated andsensitive construction.

[0004] The problem on which the invention is based consists in providingan electrode of the generic type described in the introduction which canbe used to produce holes or bores with a very small diameter incombination with a simple electrode construction. Moreover, it isintended to provide a process for producing an electrode of this type.

[0005] According to the invention, the problem is solved by the factthat the (electrode) tube consists of a metal with a substantiallyamorphous structure, is electrically conductive and thereforesimultaneously serves as an electrical conductor for applying a charge,and is provided on its outer surface, at least in sections, with anonconductive insulating layer.

[0006] An advantage of an electrode made from a tube of this type isthat metals of substantially amorphous structure, what are known asmetallic glass materials, can be processed to form tubes with relativelysmall external diameters in the range from 0.2 mm to 0.04 mm. Tubesproduced from metal with a substantially amorphous structure areresistant to corrosion and wear and have a virtually smooth and flawlesssurface, along which the flow of electrolyte is optimal. Moreover, it ispossible to dispense with the introduction of a metallic conductor, suchas a platinum wire, since the negative charge of a DC source is appliedto the tube itself. The positive charge of the DC source is applied tothe workpiece which is to be machined.

[0007] The external diameter of the tube may be at most slightly lessthan 0.2 mm, and is preferably in the range from 0.2 mm to 0.04 mm, sothat it is substantially possible to produce holes or bores with adiameter of 0.2 mm and below.

[0008] The tube may be of any desired cross-sectional geometry and canbe adapted to various applications, so that it is also possible forholes which are not circular in cross section to be formed in theworkpiece.

[0009] The tube may furthermore consist of a metallic solid glass, suchas a ZrTiNiCuBe alloy, it also being possible to use other suitablealloys and therefore other metals which are of a substantially amorphousstructure.

[0010] The nonconductive insulating layer may be a layer based on AlONor TiAlON or organic, such as coating, materials, or inorganic oxideceramic, the layer thickness of this layer being very small. Thethickness of the insulating layer may be less then 10 μm and isgenerally between 4 μm and 10 μm. With an insulating layer based onTiAlON, the layer may be applied to the tube made from a metal ofsubstantially amorphous structure by sputtering or vapour deposition.

[0011] The entire outer surface of the tube may be provided with anonconductive insulating layer, in order to prevent electrochemicalcorrosion or additional undesired erosion during fine-boring at the wallof the bore formed in the workpiece.

[0012] Those sections of the tube which are provided with thenonconductive insulating layer may be provided with an electricallyconductive metal or graphite layer, to which, as a so-called protectivecurrent electrode, an opposite charge to that of the tube made from ametal of substantially amorphous structure can be applied.

[0013] According to the invention, the solution to the problem relatingto the process for producing an electrode for electrochemicalfine-boring is characterized in that an electrically conductive metalwith a substantially amorphous structure is provided as material for theelectrode tube, the electrode tube is drawn from a semi-finished tube oflarger external diameter to a smaller external diameter by glassdrawing, and a nonconductive insulating layer is applied at least tosections of its outer surface. Further configurations of the electrodeaccording to the invention and of the process according to the inventionare described in the subclaims.

[0014] In the text which follows, the invention is explained in moredetail on the basis of exemplary embodiments and with reference to adrawing, in which:

[0015]FIG. 1 shows an electrochemical boring arrangement with anelectrode which is known from the prior art;

[0016]FIG. 2 shows an electrochemical fine-boring device according toone configuration of the electrode according to the invention; and

[0017]FIG. 3 shows an electrochemical fine-boring arrangement accordingto an alternative configuration of the electrode according to theinvention.

[0018]FIG. 1 diagrammatically depicts an electrochemical boringarrangement which is known from the prior art, with an electrode 1comprising a glass tube 2 and a platinum wire 3 which is arrangedtherein and serves as an electrical conductor. An electrolyte 4 flowsthrough the glass tube 2 and, at the end side, emerges in a region of aworkpiece 5 which is to be machined by electrochemical boring. A DCsource 12 is used to apply opposite charges to the platinum wire 3 andthe workpiece 5, so that the chemical reaction which is required for theelectrochemical boring takes place with the exchange of electrons. Anegative charge is applied to the platinum wire 3, and a positive chargeis applied to the workpiece 5. During the boring, the electrode 1 ismoved in the direction of arrow V.

[0019] When using a glass tube, the bores 13 which are to be produced inthe workpiece 5 using the electrochemical boring process are limited toa minimum diameter of 0.2 mm. Moreover, the structure of the electrode 1comprising the glass tube 2 and the platinum wire 3 arranged therein iscomplicated and sensitive.

[0020]FIG. 2 diagrammatically depicts an electrochemical fine-boringarrangement according to one configuration of the electrode according tothe invention, which is denoted overall by 6 and substantially comprisesan (electrode) tube 7 made from a metal of substantially amorphousstructure, such as for example a ZrTiNiCuBe alloy. The tube 7 has anexternal diameter D which is less than 0.2 mm and, depending on the sizeof the desired bore 13 in the workpiece 5, is in the range between 0.2mm and 0.04 mm. Opposite electric charges are applied to the electrictube 7 and the workpiece 5 by a DC source 12, a negative charge beingapplied to the tube 7 and a positive charge being applied to theworkpiece 5.

[0021] An electrolyte 4 flows through the tube 7 from a holding device 8to an opening 9 of the tube 7, where it comes into contact with thatarea of the workpiece 5 which is to be eroded by electrochemical boring,in order to erode the material of the workpiece 5 by means of a standardchemical reaction with exchange of electrons. The tube 7 is secured in acustomary way in the holding device 8, through which the electrolyte 4is fed to the tube 7.

[0022] In the present configuration, a nonconductive insulating layer 10is applied to the entire outer surface of the tube 7, in order toprevent electrochemical corrosion or an additional, undesired erosionduring fine-boring at the wall of the bore 13. The insulating layer 10ensures that there is no current passing through at this point andtherefore there is neither corrosion nor undesirable erosion ofmaterial. The chemical reaction takes place exclusively in the region ofthe opening 9 of the tube 7 and leads to erosion of material and to thebore 13 becoming deeper. The insulating layer 10 is a layer of a mixedoxide, for example based on TiAlON, which has been applied by sputteringor vapour deposition and has a layer thickness which is generally lessthan 10 μm and therefore only-slightly increases the desired smallexternal diameter of the tube 7.

[0023]FIG. 3 diagrammatically depicts an alternative configuration ofthe electrode according to the invention, which is denoted overall by 6and in which an (electrode) tube 7 consists of an electricallyconductive metal which is of substantially amorphous structure. The tube7 is held in a holding device 8, from which it is supplied with anelectrolyte 4. The electrolyte 4 flows through the tube 7 and emerges,at an opening 9 of the tube 7, at that area of a workpiece 5 which is tobe machined. A negative charge is applied to the electrically conductivetube 7 via a DC source 12, and a positive charge is applied to theworkpiece 5 in which a bore 13 is to be made by electrochemicalfine-boring, likewise via the DC source 12. A nonconductive insulatinglayer 10 based on an oxide ceramic, such as for example Al₂O₃, isapplied to an outer surface of the tube 7, so that there is no currentpassing through this layer. The intention at this point is, for example,to prevent electrochemical corrosion or additional, undesired erosion ofmaterial in the region of the wall of the bore 13 in the workpiece 5.

[0024] The tube 7 has an external diameter D of 0.09 mm, so that a bore13 of slightly larger than 0.09 mm is produced, taking into account thethickness of the insulating layer 10 of approximately 7 μm Therefore,the material is eroded exclusively in the region of the opening 9 of thetube 7 as a result of a customary chemical reaction with exchange ofelectrons, since the electrolyte is connected firstly to theelectrically conductive tube 7 and secondly to the workpiece 5, which islikewise electrically conductive. During the boring operation, theelectrode 6 is moved in the direction of arrow V, in order to achievethe desired depth of the bore 13. On account of the insulating layer 10,there is no undesirable erosion of material at the wall of the bore 13.

[0025] In the present embodiment, an electrically conductive metal layer11 is applied to the insulating layer 10 as a so-called protectivecurrent electrode, to which a positive charge, i.e. an opposite chargeto that applied to the tube 7, is applied via a DC source 14, in orderin this way to additionally prevent the partial etching or undesiredwidening of the wall of the bore 13 in the workpiece 5. Alternatively, adifferent electrically conductive layer 11, such as for example agraphite layer, may also be applied as protective current electrode. Theopposite, negative charge is applied to the workpiece 5 by the DC source14.

[0026] The electrode 6 for electrochemical fine-boring in workpieceswhich is illustrated in FIG. 2 and 3 is produced in such a manner thatthe material used for the electrode tube 7 is an electrically conductivemetal of substantially amorphous structure, i.e. what is known as ametallic glass material, such as for example a ZrTiNiCuBe alloy, and theelectrode tube 6 is drawn from a semi-finished tube of larger externaldiameter to an external diameter D in the range from 0.2 mm to 0.04 mmby glass drawing in an inert gas atmosphere. Then, an insulating layer10 is applied to the outer surface of the electrode tube 6 produced inthis way, so that during the fine-boring of a bore 13 into a workpiece5, there is passage of current only in the region of the opening 9 ofthe electrode tube 6, on account of the electrolyte 4 emerging at thatlocation. The insulating layer 10 substantially comprises AlON, TiAlONor an oxide ceramic. In the case of the electrode 6 illustrated in FIG.3, an electrically conductive metal or graphite layer 11 is then alsoapplied to the insulating layer 10, for example by sputtering or vapourdeposition, this layer serving as a protective current electrode.

1. Electrode for the electrochemical fine-boring of workpieces, comprising an (electrode) tube (6) for an electrolyte (4) to pass through to reach a workpiece (5) which is to be machined, and an electric conductor which is connected to the electrolyte (4), characterized in that the tube (6) consists of a metal with a substantially amorphous structure, is electrically conductive and is provided on its outer surface, at least in sections, with a nonconductive insulating layer (10).
 2. Electrode according to claim 1, characterized in that the external diameter (D) of the tube (6) is between 0.2 mm and 0.04 mm.
 3. Electrode according to claim 1 or 2, characterized in that the tube (6) has any desired cross-sectional geometry.
 4. Electrode according to one or more of the preceding claims, characterized in that the tube (6) consists of a ZrTiNiCuBe alloy.
 5. Electrode according to one or more of the preceding claims, characterized in that the insulating layer (10) substantially comprises AlON or TiAlON or an organic base, such as coatings, or an inorganic oxide ceramic.
 6. Electrode according to one or more of the preceding claims, characterized in that the thickness of the insulating layer (10) is in the range from 4 μm to 10 μm.
 7. Electrode according to one or more of the preceding claims, characterized in that the outer surface of the electrode (6) is substantially completely provided with the insulating layer (10).
 8. Electrode according to one or more of the preceding claims, characterized in that an electrically conductive metal or graphite layer (11) is applied at least to sections of the insulating layer (10).
 9. Process for producing an electrode for electrochemical fine-boring, the electrode comprising an electrode tube (6) for an electrolyte (4) to pass through to reach a workpiece (5) which is to be machined, and an electrical conductor which is connected to the electrolyte (4), characterized in that an electrically conductive metal with a substantially amorphous structure is provided as material for the electrode tube (6), the electrode tube (6) is drawn from a tube of larger external diameter to a smaller external diameter (D) by glass drawing, and a nonconductive insulating layer (10) is applied at least to sections of its outer surface.
 10. Process according to claim 9, characterized in that the glass drawing is carried out in an inert gas atmosphere.
 11. Process according to claim 9 or 10, characterized in that the tube of larger external diameter is drawn to an external diameter (D) of the electrode tube (6) which lies in the range from 0.2 mm to 0.04 mm.
 12. Process according to one or more of claims 9 to 11, characterized in that an electrically conductive metal or graphite layer (11) is applied at least to sections of the insulating layer (10). 